a. Field of the Invention
The present invention pertains to data transmission systems and specifically to serial data transmissions with elasticity buffers.
b. Description of the Background
Serial communications are commonly used between electronic devices. In cases where two devices must communicate through a continuous serial protocol but the devices do not share a common clock, an elasticity buffer may be provided at one or both ends of the communications link. An elasticity buffer may add or remove null characters from the serial data stream to compensate for slight mismatches between the clock signals of the two devices.
During normal start up and initialization of the serial communication, the serial devices and their associated elasticity buffers begin communication in a known state. Since the elasticity buffer operates by having asynchronous read pointers and write pointers, it is possible that when an elasticity buffer is stopped and restarted that the offset between the read and write pointers may shift. Thus, after repeated stopping and restarting of an elasticity buffer, the pointers of the elasticity buffer may shift to the point where the read and write pointers overlap, causing the elasticity buffer to potentially produce noisy and unreliable data.
When one of the devices is not transmitting, noise on the transmission line may be picked up by the interface containing the elasticity buffer. The noise may be received and processed by the elasticity buffer, potentially causing downstream problems.
In an example of a serial communication between a disk drive and the main processor of a portable computer, a constant serial communication may exist between the disk drive and the main processor. Such a communication may incorporate one or more elasticity buffers. During a period of inactivity, the disk drive may be shut down to conserve electrical power and also may cease transmitting on the serial communications bus. During reestablishment of the serial communication, any problems with the pointers of the elasticity buffer may cause some problems in properly establishing communications. After repeated cessations of transmissions, the chances increase that the elasticity buffer pointers may be misplaced and prone to errors.
It would therefore be advantageous to provide a system and method for pausing an elasticity buffer when there is no activity on a serial communications bus and properly restarting the elasticity buffer when serial communication is reestablished.